<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <!-- 输入月份，显示当月的天数 -->
    <script>
        var month=parseInt( prompt("请输入你的月份"));
      
        switch(month){
            case 1:
            case 3:
            case 5:
            case 7:
            case 8:
            case 10:
            case 12:
            alert("有31天");
            break;
           
            case 4:
            case 6:
            case 11:
            alert("有30天");
            break;
            case 2:
            alert("有28天");
          
                break;
                default:
                    alert("不在输入的范围");
                    break;
             
        }
    </script>
</body>
</html>